Process for the preparation of aluminum oxide film using dialkylaluminum alkoxide

ABSTRACT

An aluminum oxide film is economically and conveniently deposited on a substrate by a process which comprises vaporizing a dialkylaluminum alkoxide compound at a temperature ranging from 0 to 25° C. and contacting the resulting vapor with said substrate heated to a temperature ranging from 300 to 600° C.

FIELD OF THE INVENTION

The present invention relates to a process for coating a substrate withan aluminum oxide film by chemical vapor deposition using adialkylaluminum alkoxide compound as an aluminum source.

BACKGROUND OF THE INVENTION

There have hitherto been reported a number of chemical vapor deposition(CVD) methods for the preparation of an aluminum oxide film. Thesemethods are well summarized in recent review by E. Fredriksson et al.,"Chemical Vapour Deposition of Aluminum Oxides from Various GasMixture," and J. Chemical Vapor Deposition, 1, 333-417 (1993) as well asin Korean translation of "CVD Handbook" pp 665-689 (Bando PublishingCo., Seoul, Korea, 1993). Aluminum trichloride and triisopropoxide havebeen most commonly used as aluminum sources in the CVD of an aluminumoxide film due to their low cost and ready availability. Theseconventional aluminum sources have low vapor pressures and are usuallyheated to higher than 100° C. to generate a vapor stream to be used in aCVD process.

Further, trialkylaluminums have been used in the CVD of an aluminumoxide film, which are liquid at room temperature and have relativelyhigh vapor pressure. However, such trialkylaluminums do not containoxygen atoms, thus the use of an oxygen source such as O₂ or N₂ O isessential for the formation of an aluminum oxide film. Alsotrialkylaluminums are pyrophoric when exposed to air. U.S. Pat. No.4,675,089 discloses a plasma-assisted CVD method of depositing anamorphous thin film of aluminum oxide using a trialkylaluminum vapor andcarbon dioxide. However, this method requires expensive equipments toproduce plasma and have lower throughput compared to a thermal CVDmethod, thus less suitable for use in a large-scale application.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anefficient and economical process for the preparation of an aluminumoxide film suitable for a large-scale production of articles coated withaluminum oxide film.

In accordance with one aspect of the present invention, there isprovided a process for coating a substrate with an aluminum oxide film,which comprises contacting a vaporized dialkylaluminum alkoxide compoundwith said substrate heated to a temperature ranging from 300 to 600° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an Auger electron spectrum of an aluminum oxide filmdeposited on SI(100) at 400° C. using diethylaluminum isopropoxide inaccordance with Example 6 of the present invention; and

FIG. 2 shows an Auger depth profile of the film obtained in Example 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is characterized in that a dialkylaluminumalkoxide is used as an aluminum source in the chemical deposition of analuminum oxide film.

The dialkylaluminum alkoxide useful for practicing the present inventionis a material which has a high vapor pressure sufficient to vaporizeunder an ambient condition, i.e., 0.06 to 0.5 mmHg at a temperatureranging from 0 to 25° C. The dialkylaluminum alkoxide compound suitablefor use in the present invention is represented by the followingformula:

    R.sup.1.sub.2 AlOR.sup.2

wherein R¹ and R² are each independently a C₁₋₁₀ alkyl group.

The dialkylaluminum alkoxide compound according to the present inventionmay be prepared by reacting an alkylaluminum with an alcohol at a lowtemperature by a conventional method, e.g., as is described by Paul S.Coan, et al. in Organometallics, 8, 2724 (1989), or by reacting analkylaluminum with an aluminum alkoxide in a molar ratio of 2:1 at roomtemperature.

The preferred dialkylaluminum alkoxide compound in practicing thepresent invention may be dimethylaluminum isopropoxide,diethylaluminumisopropoxide, dimethylaluminum t-butoxide and a mixturethereof. Under an ambient condition, dimethylaluminum isopropoxide is aliquid, whereas diethylaluminum isopropoxide and dimethylaluminumt-butoxide are gel-like solids.

In accordance with the present invention, the dialkylaluminum alkoxidecompound is vaporized at an ambient temperature ranging from 0 to 20° C.and the vapor thereof is then contacted with the surface of a substrateheated at a temperature ranging from 300 to 600° C. to deposit analuminum oxide film thereon.

The vaporization of dialkylaluminum alkoxide compound may be carried outin a reactor which is preferably maintained at an internal pressure of10 to 50 mbar.

The substrate which may be used in practicing the present invention isan inorganic solid which is stable under the CVD condition and examplesthereof include glass, quartz, silicon, gallium arsenide, sapphire,alkali metal niobate, alkaline earth metal titanate, gallium nitride,niobium nitride and the like, among which silicon single crystal ispreferred when the coated substrate is intended for electronicapplications.

The following Preparatives and Examples are provided for the purposes ofillustrating certain aspects of the present invention only; they are notto be construed as limiting the scope of the present invention in anyway.

Preparative 1: Synthsis of dimethylaluminum t-butoxide

To 2.07 g (28.7 mmol) of trimethyl aluminum dissolved in 30 ml of dryethyl ether was added 2.13 g (28.7 mmol) of t-butanol at -70° C., andthe resulting mixture was warmed to room temperature while stirring andthe solvent was evaporated off under a reduced pressure. The residue wassublimed to obtain 2.16 g (16.6 mmol, 58% yield) of the title compoundin the form of a gel-like solid. ¹ H NMR analysis in benzene-d₆ of thecompound obtained showed peaks at δ-0.42(s, Al(CH₃)₂, 6H) and 1.15(s,OC(CH₃)₃, 9H).

Preparative 2: Synthsis of dimethylaluminum isopropoxide

To 2.75 g (38.1 mmol) of trimethyl aluminum was added 3.90 g (19.1 mmol)of aluminum isopropoxide which was previously purified by distillationunder a reduced pressure to obtain 12.52 g (108 mmol, 87% yield) of thetitle compound in the form of a colorless liquid that boils at atemperature ranging from 68 to 72° C. at 10 mmHg. ¹ H NMR in benzene-d₆analysis of the compound obtained showed peaks at δ-0.47(s, Al(CH₃)₂,6H), 0.99(d, OCH(CH₃)₂, 6H) and 3.84(heptet, OCH(CH₃)₂, 1H).

Preparative 3: Synthsis of diethylaluminum isopropoxide

To 1.21 g (10.6 mmol) of triethyl aluminum (93% purity, Aldrich ChemicalCo.) was added 1.08 g (5.3 mmol) of aluminum triisopropoxide which waspreviously purified by distillation under a reduced pressure, and theresulting mixture was stirred for 24 hours and the mixture was sublimedto obtain 1.89 g (13.5 mmol, 85 yield as diethylaluminum isopropamide)of the title compound in the form of a gel-like solid.

EXAMPLE 1

0.05 g of dimethylaluminum t-butoxide prepared in Preparative 1 wasvaporized at 0° C. and the vapor thereof was conveyed to a Si(100)substrate preheated to 400° C. to conduct the chemical vapor depositionfor 3 hours. The X-ray photoelectron spectrum of the deposited filmshowed peaks corresponding to oxygen and aluminum as well as carbon, butnot the peaks for silicon. This observation shows that the surface ofthe silicon substrate is completely covered by an aluminum oxide film.

EXAMPLE 2

The procedure of Example 1 was repeated except that the Si(100)substrate was preheated to 300° C. and the chemical vapor deposition wascarried out for 1 hour. The X-ray photoelectron spectrum of thedeposited film showed peaks corresponding to oxygen and aluminum as wellas carbon, but not the peaks for silicon.

EXAMPLE 3

0.1 g of dimethylaluminum isopropoxide prepared in Preparative 2 wasvaporized at room temperature and the vapor thereof was transported to aSi(100) substrate preheated to 350° C. to conduct the chemical vapordeposition for 5 hours. The X-ray photoelectron spectrum of thedeposited film showed peaks corresponding to oxygen and aluminum as wellas carbon, but not the peaks for silicon.

EXAMPLE 4

0.1 g of diethylaluminum isopropoxide prepared in Preparative 3 wasvaporized at room temperature and the vapor thereof was brought intocontact with a Si(100) substrate preheated to 350° C. to conduct thechemical vapor deposition for 2 hours. The X-ray photoelectron spectrumof the deposited film showed peaks corresponding to oxygen and aluminumas well as carbon, but not the peaks for silicon.

EXAMPLE 5

0.1 g of dimethylaluminum isopropoxide prepared in Preparative 2 wasvaporized at room temperature and the vapor thereof was carried to aSi(100) substrate preheated to 600° C. to conduct the chemical vapordeposition for 5 hours. The X-ray photoelectron spectrum of thedeposited film showed peaks corresponding to oxygen and aluminum as wellas carbon, but not the peaks for silicon.

EXAMPLE 6

0.1 g of diethylaluminum isopropoxide prepared in Preparative 3 wasvaporized at room temperature and the vapor thereof was transported to aSi(100) substrate preheated to 400° C. to conduct the chemical vapordeposition for 10 hours. The Auger electron spectrum of the depositedfilm obtained after sputtering for 6 seconds with 3.5 keV Ar⁺ ion beamis shown in FIG. 1. And Auger depth profile of the same film is shown inFIG. 2.

These data clearly indicate that the film is stoichimetric with noappreciable carbon incorporation and the composition is constant throughthe bulk of the film.

The thickness of the aluminum oxide film is estimated at 0.23 μm,assuming an etch rate of 0.83 nm/s.

In accordance with the present invention as described above, an aluminumoxide film can be conveniently and effectively deposited on a substrateby way of using a dialkylaluminum alkoxide compound as an aluminumsource. The inventive process has the advantage that gas phase mixingcan be completely avoided because no additional oxygen source isnecessary, thus a large-scale production of aluminum oxide films ispossible using simple equipments under much simplified conditions.

While the invention has been described with respect to the specificembodiments, it should be recognized that various modifications andchanges may be made by those skilled in the art to the invention whichalso fall within the scope of the invention as defined by the appendedclaims.

What is claimed is:
 1. A process for coating a substrate with analuminum oxide film, which comprises contacting a vaporizeddialkylaluminum alkoxide compound of formula (I) with said substrate:

    R.sup.1.sub.2 AlOR.sup.2                                   (I)

wherein R¹ and R² are each independently a C₁₋₁₀ alkyl group.
 2. Theprocess of claim 1 wherein the substrate is heated to a temperatureranging from 300 to 600° C.
 3. The process of claim 1 wherein thevaporization of dialkylaluminum alkoxide compound is conducted at atemperature ranging from 0 to 25° C.
 4. The process of claim 2 whereinthe dialkylaluminum alkoxide compound is selected from the groupconsisting of dimethylaluminum isopropoxide, diethylaluminumisopropoxide, dimethylaluminum t-butoxide and a mixture thereof.
 5. Theprocess of claim 4 wherein the dialkylaluminum alkoxide compound isdimethylaluminum isopropoxide.
 6. The process of claim 1 wherein thesubstrate is a silicon single crystal.